1. Field of the Invention
This invention relates to a method of automatically detecting tape defects on a magnetic tape or like tape having a fixed width, e.g., a video tape or an audio tape, and more particularly to a tape defect detection method for detecting tape defects according to light amount data obtained from the tape surface by scanning the width of the tape with a light beam.
2. Description of the Prior Art
Tape defects in audio tapes and other similar magnetic tapes, which are due to scars or scratches, deformation, or attachment of foreign particles, lead to deterioration of the tape quality. Therefore, tape defect detection is performed in the process of tape manufacture to sort out and stop shipment of tapes with tape defects.
A method of detecting tape defects is known in which a tape running in its longitudinal direction is scanned across its width with a light beam, and light reflected from the tape surface is detected. Tape defects are checked by using light amount data available from the detected reflected light.
With this prior art technique, it is possible to satisfactorily detect tape defects present in a middle portion of the width of the tape. However, it is difficult to satisfactorily detect tape defects present in places near the tape edges (hereinafter called edge portions), when scanning the width of the tape. This is due to the fact that an edge signal, produced by a great change in the amount of light reflected from the tape at the edge thereof, is difficult to distinguish from a tape defect signal. Also, overshoots occurring when the edge signal rises and falls make accurate measurement of these tape defects difficult.
Heretofore, usually only a middle portion of the width of the tape was used as a recording area, so that tape defects present near the tape edge presented no serious problems.
However, recent demands for size reduction and an increase in the density of the information stored on the recording media require the use of even tape edge portions for recording. To meet these demands, the development of a tape defect detection method, which can accurately detect tape defects present in tape edge portions, is desirable.